1. Field of the Invention
The present invention relates to a laser driving device (laser driving circuit), a laser driving method, an optical unit, and a light device.
2. Description of the Related Art
Recording and reproducing devices using a laser as a light source are used in various fields. For example, attention is directed to optical disk recording and reproducing devices (hereinafter referred to simply as optical disk devices) using a laser driving device and an optical unit and using an optical disk as a recording and reproducing medium.
As the laser used as light source, semiconductor lasers using semiconductor materials have recently been widely used in various devices because the semiconductor lasers are very small and respond to driving current at high speed.
As a writable optical disk used as a recording and reproducing medium, a phase change optical disk, a magneto-optical disk and the like are widely known. Recording, reproduction, and erasure are performed on these optical disks by changing the intensity of an applied laser beam. Generally, when information is recorded onto an optical disk, a so-called light intensity modulation system is used which forms marks and spaces on the recording medium by changing the intensity of a laser beam. At this time, the optical disk is irradiated with a laser beam of high intensity having a peak of 30 mW or more, for example. At a time of reproduction, the optical disk is irradiated with a laser beam of lower intensity (for example 1 mW) than at the time of recording so as to be able to read information without destroying recorded marks.
Mark edge recording, which provides information at positions of both edges of a recorded mark, has become mainstream on recent writable optical disks because of advantages in increasing the density of the optical disks. In the mark edge recording, a data error is caused by distortion of the shape of a mark. A write strategy technique is known in which recording power is pulse-divided, converted to multivalued levels, and controlled to perform recording with fewer errors (see for example Japanese Patent Laid-open No. 2007-141406 and “Low Noise and High-Speed Response at Highest Levels in the Field Overcoming Technological Barriers of Blu-ray Eight-Times Speed Recording and Reproduction,” CX-PAL No. 74, [online], Sony Corporation, [retrieved on Aug. 18, 2008], Internet <URL: http://www.sony.co.jp/Products/SC-HP/cx_pal/vol74/pdf/featuring2_bd.pdf>).